Recording materials which employ an electron-donating colorless dye and an electron-accepting compound are well known. Examples of such recording materials are pressure-sensitive papers, heat-sensitive papers, light-sensitive heat-sensitive papers, electroconductive heat-sensitive papers, heat-sensitive transfer papers, and the like. These are described in detail, for example, in British Patent 2,140,449, U.S. Pat. No. 4,480,052, U.S. Pat. No. 4,436,920, JP-B-60-23992 (the term "JP-B" as used herein means an "examined Japanese patent publication"), JP-A-57-179836 (the term "JP-A" as used herein means an "unexamined published Japanese patent application"), JP-A-60-123556, JP-A-60-123557, and so forth.
In particular, heat-sensitive recording materials have been extensively studied to improve (1) developed color density and color developing sensitivity, and (2) fastness of the color-developing materials.
At the moment, however, heat-sensitive recording materials still have disadvantages in that the non-image portions become colored or the image portions fade due to the action of light after the materials are exposed to sunlight for a long time or are posted in offices for a long term.
Various methods have been investigated to lessen the discoloration of the non-image portions and fading of the image portions. (See JP-A-50-104650, JP-A-58-087093, JP-A-60-203487, JP-A-61-242878 and JP-A-61-193883.) However, satisfactory improvement has not been achieved.